In a design process of an audio player, the frequency response of the audio signal is commonly needed to be adjusted to compensate the frequency response of the speaker as the frequency response curve of the speaker is uneven, to achieve a much flatter frequency response, and a better sound quality.
Normally, the adjusting process is conducted in an anechoic room (a room without sound reflection), so that it is just in the anechoic room the frequency response characteristic obtained is flat. However, actually in user's rooms, as the walls and the household products may absorb, diffract, and reflect the sound waves (different affecting to sound waves having different frequencies), the frequency response characteristic which is flat during in the anechoic room, would be uneven during in user's rooms. In addition, the above adjusting method only compensates the unevenness of the speaker, but cannot compensate the uneven frequency response characteristic of human's ears (human ears' equal-loudness contour reflects the characteristic), as different people have different equal-loudness contours (race, gender, and age can induce the difference). Therefore, the sound response characteristics of the speaker obtained by user after being adjusted through the above method are still not flat enough, thus causing the sound being still unsatisfactory.